Re: [svgwg] Opacity properties should affect nothing but opacity

While I was working on http://codepen.io/TobiReif/pen/ZpERON , at some
 point I came across the issue - I set opacity (from CSS IIRC) and one
 or more items were suddenly overlapped by others. That is very bad 
SVG-user experience design. (Not sure why the issue appeared in an SVG
 using SVG1, perhaps the browser had jumped ahead to SVG2 in this 
aspect.)

Regarding CSS:

See https://github.com/w3c/csswg-drafts/issues/464 .

It is not sensible to spec the same issue in SVG 2, because it would 
not be SVG-user friendly. It would cause the same problems and 
confusion caused by the behaviour of CSS. People even use 
"opacity:0.99" hacks ... 
https://philipwalton.com/articles/what-no-one-told-you-about-z-index/

> is not something that will confuse authors that don't use z-index.
...
> I don't think the extra knowledge required to use z-index is that 
onerous.

It is! The user of your spec would use "z-index" to change the 
stacking order, and would use opacity properties to change the opacity
 - requiring the user of your spec to know that setting/changing 
"opacity" affects anything other than opacity is (frankly speaking) 
bad API design. The user might simply (while setting/changing nothing 
but opacity values) get bitten by the issue, without knowing the 
cause(!)

I've been using z-index (in CSS) for many years, and until recently I 
never knew about the very surprising and very problematic fact that 
opacity properties can change stacking order.

Please make sure that the presence or absence of any opacity values 
never affects anything except opacity. No matter any z-index values.

Please re-open this issue ticket, please reconsider, and please 
convince the SVG WG.

The normal opacity properties should affect nothing but opacity. You 
then could consider offering additional options/properties eg because 
of performance considerations.


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Received on Monday, 12 September 2016 10:48:51 UTC